Connecting WRT54G2 with a Arris TM602G/CT Modem?

First off I have Comcast internet serivce. I used to have AT&T but we switched from them. AT&T's modem worked perfectly fine but it's this Arris one thats giving me a hard time. I've searched a lot and I've also tried a lot of different remedies but nothing seems to work. On the Linksys EasyLink Advisor page the correct router doesn't even show up it just says Gateway, the internet circle is green, but the line connecting to modem to the router is red. The thing is that the interent is still working with the desktop, it just won't let me connect anything wireless to it. If I try to add a device to it only the wired option is choosable. I can even find my network on my laptop secured and everything but it asks me for the pin to configure it instead of the passphrase. Any help is appreciated thanks.